The Ten Myths of DAB

[JFLL]

... A series of 'up-to-the-minute' roof aerials over the years has never delivered ideal FM reception where I live, always some interference, and never possible to listen in stereo. In contrast, DAB - especially after the boost in London pre-Olympics - delivers interference free sound, always at full strength, allowing listening on radios all around the place.

Rather my experience, too, Caliban, in SE3. Poor FM (altho’ we’re only about 5 miles from Crystal Palace – might be the aerial, I suppose) and very good DAB. Except for one thing. From time to time there are a few seconds of what I can only call ‘sonic gobbledegook’ on just one of our two Pure machines – very startling in the middle of a piece of music.

[Nick Armstrong]

Rather my experience, too, Caliban, in SE3. Poor FM (altho’ we’re only about 5 miles from Crystal Palace – might be the aerial, I suppose) and very good DAB. Except for one thing. From time to time there are a few seconds of what I can only call ‘sonic gobbledegook’ on just one of our two Pure machines – very startling in the middle of a piece of music.

I know what you mean, we used to get the odd 'electro-gurgle' as the signal strength used to vary and occasionally drop out. Since the boost in April or May, we get full signal, all bars on the little logo, all the time.

[Resurrection Man]

....Poor FM (altho’ we’re only about 5 miles from Crystal Palace – might be the aerial, I suppose) ....

Or more likely it is because there is no FM transmission from CP.


Wrotham is your local Tx.

[Nick Armstrong]

Or more likely it is because there is no FM transmission from CP.

Back of the net... !

[JFLL]

Or more likely it is because there is no FM transmission from CP.
Wrotham is your local Tx.

Thanks, RM. That explains a few things -- it's the other d**ned direction!

[:egg on face emoticon -- Caliban?]

[Nick Armstrong]

[:egg on face emoticon -- Caliban?]

Hmm.... not egg... but will this do?

[Gordon]

Or more likely it is because there is no FM transmission from CP.


Wrotham is your local Tx.

Er, actually CP IS an FM station:

Crystal Palace: 98.5R1 88.8R2 91.0R3 93.2R4
Vert Pol [ie a relay]
Power 4kW
Map Ref: TQ339712

http://www.bbc.co.uk/reception/transmitters/radio/england_fm.shtml#Wrotham

[amateur51]

Er, actually CP IS an FM station:

Crystal Palace: 98.5R1 88.8R2 91.0R3 93.2R4
Vert Pol [ie a relay]
Power 4kW
Map Ref: TQ339712

http://www.bbc.co.uk/reception/trans....shtml#Wrotham

[JFLL]

Er, actually CP IS an FM station:

Crystal Palace: 98.5R1 88.8R2 91.0R3 93.2R4
Vert Pol [ie a relay]
Power 4kW
Map Ref: TQ339712

http://www.bbc.co.uk/reception/trans....shtml#Wrotham

[:egg off face emoticon ?]

[Gordon]

[:egg off face emoticon ?]

Seriously though if you are having reception troubles obviously check by the tuner readout the frequency that your tuner is using and that will tell which transmitter you are on. If it's a weak signal and you have an aerial outside then its polarisation matters. CP is vertical and low power - 4kW - but nearer with Wrotham some distance away - but much more powerful at 250kW - and mixed [ie half power in Horizontal and half in Vertical]. South London is hilly and so precise location and local conditions will determine the best site to aim at. Get your OS map out!!

[Resurrection Man]

LOL...I just went with the BBC website here http://www.bbc.co.uk/reception/transmitters/radio/ No sign of CP there!

Even so..... 4kW ? I've got an electric heater radiates more than that

'Yes', 'e said, 'I gets a cracking FM signal with my 367 element Yagi on the 100ft tower.

[Nick_G]

LOL...I just went with the BBC website here http://www.bbc.co.uk/reception/transmitters/radio/ No sign of CP there!

Even so..... 4kW ? I've got an electric heater radiates more than that

'Yes', 'e said, 'I gets a cracking FM signal with my 367 element Yagi on the 100ft tower.

That map only shows the main sites, not the relays. CP is a relay of Wrotham and it was installed to improve reception for some who have problems with the signal from Wrotham in some parts of London.

Regards,
Nick

[JFLL]

Thanks, Gordon, RM and Nick, that’s interesting. Actually we haven’t got an outside radio aerial, so I suppose it’s not surprising that FM reception isn’t brilliant, either on 91.0 (Crystal P.) or 91.3 (Wrotham). The FM tuner plugged into our good speakers in the sitting-room happens to get the worst reception, being in an inner corner, so we tend to play R3 in that room through our speakers via our Freeview TV receiver (recordable, too) which is linked to an outside TV aerial, of course. Also, DAB is crystal-clear on the two portable Pure radios in other rooms without an outside aerial, and by and large we’re happy with that.

[An_Inspector_Calls]

Actually, a 4 kW VHF radio transmitter is quite powerful - VHF aviation transmissions are usually less than 10 W and can reach over a 100 miles.

Caliban and JFLL's experiences are the same as mine. The trouble with VHF transmissions is that they travel rather well, not just by line-of-sight but also ground wave. I can receive Holme Moss, well over a 100 miles away and below the horizon (t'other side of the Peninnes). But then an FM receiver needs a good FM signal to produce stereo sound with a 60 dB signal to noise ratio. So you select a sensitive receiver and point a good aerial at your local transmitter, as I did. But then my local is just 10 degrees azimuth off Holme Moss! OK, more elements to the aerial, but VHF Yagis are huge - the size of the bed - and it's difficult to narrow their reception lobe. Ah, look, a receiver costing even more with controllable IF bandwidth, that'll do . . . And so it goes on.

DAB, Freeview: stick a screwdriver in the aerial socket, job done!

[Bryn]

DAB, Freeview: stick a screwdriver in the aerial socket, job done!

Rubbish. Even wet brickwork can seriously attenuate an already marginal DAB signal enough for the boiling mud to start or for it to totally fail to resolve. I, for instance, need a rooftop dipole to get decent, reliable DAB reception here in RG12.